1. Statement of the Technical Field
The inventive arrangements relate to communication systems, and more particularly to fault tolerant simulcast communication systems.
2. Description of the Related Art
Simulcast systems are frequently used in critical public safety communication applications. In a simulcast communication system, multiple remote transmit sites operate under the command of a common control point. The control point causes each transmit site to broadcast the same signal, on the same RF frequency, at the precise time necessary for simultaneous arrival of the signal in overlap regions. This arrangement allows a simulcast communication system to provide reliable communication over a broader geographic area than would otherwise be possible with a single transmitting station. Simulcast systems have many advantages but must contend with the problem of time delay interference (TDI), which involves signals from one transmit site destructively interfering with signals from other transmit sites. In order to control this problem, each remote transmit site will include a very precise timing system to facilitate synchronization of RF transmissions from each of the multiple transmit sites. Still, timing systems are a potential point of failure in simulcast communication systems and when a timing system fails, the remote transmit site can no longer function as part of the simulcast system. When this happens the malfunctioning transmit site will frequently engage a bypass mode of operation. In a bypass mode, the site functions in a way that is similar to an ordinary trunked repeater site to facilitate continued communications among mobile units within a coverage area of the malfunctioning transmit site. In this bypass mode, the transmit site operates in a way that is substantially autonomous relative to the remainder of the simulcast system. However, a dispatch console under these conditions will generally lose the ability to communicate with mobile units through the malfunctioning transmit site. The dispatch operator can revert to an auxiliary radio for communicating through the remote transmit site, but in so doing will lose the benefit of many advanced functions provided by the dispatch console.